a. Field of the Invention
The instant invention relates to assemblies and methods for puncturing, or piercing, tissue within the body, including, for example, transseptal access systems and methods for accessing the left atrium.
b. Background Art
The human heart includes a right ventricle, a right atrium, a left ventricle and a left atrium. The right atrium is in fluid communication with the superior vena cava and the inferior vena cava. The tricuspid valve separates the right atrium from the right ventricle. The right atrium is separated from the left atrium by the intra-atrial septum. The intra-atrial septum includes a thin membrane known as the fossa ovalis. The human heart further includes the left superior pulmonary vein, the left pulmonary artery, the arch of the aorta, and the right pulmonary artery.
A wide variety of diagnostic and therapeutic procedures have been developed in which a catheter is transluminally advanced within a guide sheath or over a guidewire into various chambers and across valves of the heart. The most difficult chamber of the heart to access with a catheter may be the left atrium. Access to the left atrium through the pulmonary artery may not be possible. Approaches from the left ventricle are difficult, may cause arrhythmias and may present difficulty in obtaining stable catheter positioning. Accordingly, one of the most common approaches used by electrophysiologists to gain access to the left atrium is through puncture of the intra-atrial septum. This procedure is commonly referred to as transseptal catheterization. The manual puncture of the intra-atrial septum is generally performed at the location of the fossa ovalis.
The objectives of left atrial access can be either diagnostic or therapeutic. One therapeutic use is electrophysiological intervention, e.g., left atrial ablation. Catheter ablation involves the placement of energy (typically RF) through a catheter, into various locations of the heart to eradicate inappropriate electrical pathways affecting the heart function. When these locations are in the left atrium, the catheter through which the RF generator is placed typically is itself placed through transseptal catheterization.
In most cases, transseptal catheterization is facilitated with tools such as a sheath, dilator, and a needle. The conventional approach for trans septal catheterization follows a number of steps. First, a guidewire is introduced into the femoral vein (or other pathway of choice) and is manipulated into the inferior vena cava (IVC). Second, a sheath typically having a dilator disposed therein are inserted over the proximal end of the guidewire and are fed into the IVC. At this point, the guidewire is removed. Third, a needle is advanced through the inner lumen of the dilator with the distal end still inside of the distal end of the dilator. In what is typically referred to as a trans septal approach, a needle may be pressured though the intra-atrial septum between the right and left atria by a physician using the needle. With the needle still contained within the distal end of the dilator, the needle is maneuvered into the right atrium and pulled along the septal wall of the right atrium until it is proximate the fossa ovalis. The needle is then advanced forward by the physician through the dilator to puncture the septal wall. Upon confirmation of the puncture, the dilator and sheath can then be fed through the septal wall over the needle, thereby accessing the left atrium. The needle opening may be expanded so that various tools (e.g., sheaths or catheters) may be pressed through the opening and have access to the left atrium and the pulmonary veins. After the tools are positioned in the left atrium, various procedures, such as ablation and mapping, may be performed therein.
As described above, conventional methods of gaining access to the left atrium involve manually puncturing the intra-atrial septum at the location of the fossa ovalis using a needle. Although this method is frequently used and clinically accepted, there are some potential risks to the patient. In particular, complications may be encountered if the septal tissue is exceptionally thick or exhibits increased compliance.
The septal wall, and particularly the fossa ovalis, is a compliant structure. Generally, the fossa ovalis is even more compliant than the septal wall. Consequently, when a needle contacts the septal tissue, the contact force causes the tissue to stretch and displace in the direction of the applied force. The displacement of the tissue may be proportional to the applied force and the compliance of the tissue (e.g., displacement per unit force). Accordingly, the greater the applied force, the greater the displacement. When the contact force applied by the needle against the tissue is gradually increased (thereby increasing the contact pressure, which is force divided by area), the tissue displaces more and more in response to the force until the force is high enough to create a contact pressure that exceeds the breaking stress of the tissue wall, thereby causing a hole in the wall allowing the needle to pierce through the wall. In order to improve the safety and efficacy of transseptal puncture, it may be desirable to increase the contact pressure (e.g., beyond the breaking stress of the fossa ovalis), while minimizing the displacement of the compliant fossa ovalis.
In the case of a thick and/or fibrous septum, a physician may need to apply a large force to the needle to advance the needle through the septum. When the needle exits the septal tissue, it may be difficult to stop its forward movement because of the large force that has been applied. This may result in inadvertent puncture of the left atrial free wall. Similarly, in the case of exceptionally compliant septal tissue, the needle may be advanced too far into the left atrium while tenting the fossa ovalis prior to puncture. The proximity of the needle tip to the left atrial free wall may increase the risk of perforation when force is applied to gain access. As the needle exits the septal tissue it may already be in contact with additional structures within the left atrium.
It may be desirable to provide features to avoid unnecessary punctures or mistakes during operation of the transseptal needle.